Apparatus herein provides for a chosen level of power dissipation of a resistor, for example, the heating element of a thermal head assembly. The resistance of the resistor changes upon a change in temperature thereof, for example, due to increased flow of current therethrough. The apparatus includes a resistive shunt in series with the resistor, a first differential amplifier, with voltage drop across the resistor being provided to first and second input terminals of the first differential amplifier, and a second differential amplifier, voltage drop across the shunt being provided to first and second input terminals of the second differential amplifier. The output signals from the first and second differential amplifiers are provided to a voltage multiplier. The output signal from the voltage multiplier is provided to an input terminal of a power operational amplifier, and a programming sequence voltage is supplied to another input terminal of the power operational amplifier. The output signal from the power operational amplifier is provided to the resistor.
Legal claims defining the scope of protection, as filed with the USPTO.
1. Apparatus for providing a chosen level of power dissipation of a resistor, the resistance of the resistor changing upon change in temperature thereof, comprising: a shunt in series with the resistor; a first differential amplifier, voltage drop across the resistor being provided to first and second input terminals thereof; a second differential amplifier, voltage drop across the shunt being provided to first and second input terminals thereof; a voltage multiplier having first and second input terminals which are connected to the respective output terminals of the first and second differential amplifiers; a power operational amplifier, an output terminal of the voltage multiplier being connected to a first input terminal of the power operational amplifier; a second input terminal of the power operational amplifier provided for receiving a programming sequence voltage; an output terminal of the power operational amplifier being connected to the resistor for providing voltage thereto.
2. The apparatus of claim 1 wherein, upon a given change in current level in the resistor and shunt, the resistance of the shunt changes in a manner different from the resistance of the resistor.
3. The apparatus of claim 2 wherein the resistance of the shunt remains substantially constant upon change in current level therein.
4. The apparatus of claim 1 wherein the resistor is a heater.
5. The apparatus of claim 4 wherein the resistor is a heater of a thermal head assembly.
6. The apparatus of claim 5 wherein the resistance of the resistor is substantially greater than the resistance of the shunt.
7. The apparatus of claim 1 wherein the resistance of the resistor is substantially greater an the resistance of the shunt.
8. The apparatus of claim 7 wherein the resistor is a heater.
9. The apparatus of claim 8 wherein the resistor is a heater of a thermal head assembly.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
November 7, 2001
September 10, 2002
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